force

The Columbia Encyclopedia, 6th ed.

force

force, commonly, a "push" or "pull," more properly defined in physics as a quantity that changes the motion, size, or shape of a body. Force is a vector quantity, having both magnitude and direction. The magnitude of a force is measured in units such as the pound, dyne, and newton, depending upon the system of measurement being used. An unbalanced force acting on a body free to move will change the motion of the body. The quantity of motion of a body is measured by its momentum, the product of its mass and its velocity. According to Newton's second law of motion (see motion), the change in momentum is directly proportional to the applied force. Since mass is constant at ordinary velocities, the result of the force is a change in velocity, or an acceleration, which may be a change either in the speed or in the direction of the velocity.

Two or more forces acting on a body in different directions may balance, producing a state of equilibrium. For example, the downward force of gravity (see gravitation) on a person weighing 200 lb (91 km) when standing on the ground is balanced by an equivalent upward force exerted by the earth on the person's feet. If the person were to fall into a deep hole, then the upward force would no longer be acting and the person would be accelerated downward by the unbalanced force of gravity. If a body is not completely rigid, then a force acting on it may change its size or shape. Scientists study the strength of materials to anticipate how a given material may behave under the influence of various types of force.

There are four basic types of force in nature. Two of these are easily observed; the other two are detectable only at the atomic level. Although the weakest of the four forces is the gravitational force, it is the most easily observed because it affects all matter, is always attractive and because its range is theoretically infinite, i.e., the force decreases with distance but remains measurable at the largest separations. Thus, a very large mass, such as the sun, can exert over a distance of many millions of miles a force sufficient to keep a planet in orbit. The electromagnetic force, which can be observed between electric charges, is stronger than the gravitational force and also has infinite range. Both electric and magnetic forces are ultimately based on the electrical properties of matter; they are propagated together through space as an electromagnetic field of force (see electromagnetic radiation). At the atomic level, two additional types of force exist, both having extremely short range. The strong nuclear force, or strong interaction, is associated with certain reactions between elementary particles and is responsible for holding the atomic nucleus together. The weak nuclear force, or weak interaction, is associated with beta particle emission and particle decay; it is weaker than the electromagnetic force but stronger than the gravitational force.

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items

Items saved from this article

This article has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this article

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Buy instant access to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited article

force
Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Help
Full screen

matching results for page

    Questia reader help

    How to highlight and cite specific passages

    1. Click or tap the first word you want to select.
    2. Click or tap the last word you want to select, and you’ll see everything in between get selected.
    3. You’ll then get a menu of options like creating a highlight or a citation from that passage of text.

    OK, got it!

    Cited passage

    Style
    Citations are available only to our active members.
    Buy instant access to cite pages or passages in MLA, APA and Chicago citation styles.

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

    1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

    Cited passage

    Thanks for trying Questia!

    Please continue trying out our research tools, but please note, full functionality is available only to our active members.

    Your work will be lost once you leave this Web page.

    Buy instant access to save your work.

    Already a member? Log in now.

    Author Advanced search

    Oops!

    An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.